Hi Hemi: I'm pretty sure they are the same. I have them both, I'll see if they are interchangable tonight when I get off work, and get back to you.
Dang, that was fast! My head's still spinning! Anyhow, thanks, Bill! 3 minutes has got to be a record reply time for me...
I know for a fact that the SD45 shell is interchangeable with an SD40 mech. I've got pictures to prove it!
I will add this to the mix; the mechanisms are the same BUT on the SD45 the front flywheel is different. Instead of being the same diameter the whole length of it, about half way it steps down to a smaller diameter. This is because of the inside of the shells. I found that it will work but sometimes the flywheel will contact the inside of the shell. In other words, both frames will fit the SD40 shell. On the SD45, the flywheel (if it is the SD40 flywheel) may contact the shell. I've done this and some will and some won't. Also the black headlight plastic blocker thing is different.